1. Technical Field
The present disclosure relates to illumination systems. In particular, the present disclosure relates to a method and system for avoiding flicker (in particular 100 Hz or 120 Hz flicker) in solid state lighting (SSL) devices such as LED (Light Emitting Diode) or OLED (Organic LED) assemblies.
2. Background
For many decades GLS (General Lighting Service) or incandescent lamps have been the first choice for illumination in residential applications. These light sources could easily be coupled to the mains power supply providing an AC (alternating current) voltage of e.g. 110V or 230V at a mains frequency of e.g. 60 Hz or 50 Hz. New types of light sources like LED (light emitting diode) lamps offer very small loads (typical a factor of 10 less than the equivalent GLS lamp). However, a solid state lighting (SSL) device such as an LED or Organic LED (OLED) device requires complex driver circuitry for providing the (typically constant) load voltage to the SSL device and for providing a (typically constant) load current to the SSL device.
The driver circuitry for an SSL device should be configured to convert the AC mains voltage into the possibly constant load voltage and the possibly constant load current. In particular, the driver circuitry should be configured to control the load voltage and the load current such that the SSL device does not flicker in a manner which is visible to the human eye. Such a visible flicker may occur at a frequency of 100 Hz (for an alternating mains voltage at a mains frequency of 50 Hz) or at a frequency of 120 Hz (for an alternating mains voltage at a mains frequency of 60 Hz). Such flicker may be due to the sinusoidal waveform of the alternating mains voltage which falls below the required minimum on-voltage Von of the SSL device within each half-wave of the sinusoidal mains voltage. As a result, the SSL device is switched off at a frequency of 100/120 Hz, thereby creating an annoying flicker effect of the light source (i.e. of the SSL device). The present disclosure addresses the above mentioned technical problem of SSL devices and describes an efficient method and system for driving a SSL device without a visible flicker.